For no reflection condition, a vertically polarized wave should be incident at the interface between two dielectrics having ϵ₁ = 4 and ϵ₂ = 9, with an incident angle of 

Concept:

Brewster’s Angle:  Brewster's angle is an angle of incidence at which light with a particular polarization is perfectly transmitted through a transparent dielectric surface, with no reflection.

\(tan{\theta _i} = \sqrt {\frac{{{\epsilon_2}}}{{{\epsilon_1}}}} \)----(1)

Calculation:

For no reflection incident wave should be completely transmitted to another medium at Brewster angle.

Given:

ϵ₂ = 9, ϵ₁ = 4

From equation (1) we get,

\(tan{\theta _i} = \sqrt {\frac{9}{4}} \)

\({\theta _i} = {\tan ^{ - 1}}\frac{3}{2}\)

Note: Brewster angle does not affect S polarized waves.